Incorporate NUnit Project loader extension in msi and zip packages

[CharliePoole]

Latest NUnit project loader dev build targets the 4.0 API, so we can add it back as a bundled extension.

[CharliePoole]

This issue has been resolved in version 4.0.0-beta.1

The release is available on:
GitHub.
NuGet packages are also available NuGet.org and
Chocolatey Packages may be found at Chocolatey.org